Who can see when I've liked a photo, or when someone's liked my photo?

When you like a photo, it's visible to anyone who can see the post. Your followers may also see your username below a photo you've liked, no matter how many likes it has (example: [your username] and 12 others).

After 4 likes, photos show the number of likes, along with usernames of some people you follow who have liked it.

If your account is set to private:

Only your approved followers can see your posts, including any likes and comments